If your spouse or friends are obese, you are more likely to be overweight, too

Wednesday

Jul 25, 2007 at 12:01 AMJul 25, 2007 at 6:23 PM

A new study generated by 32 years of data compiled by the Framingham Heart Study shows that social ties are a key factor in the spread of obesity.

By Jennifer Lord

Obesity may not only run in the family - if your best friends are getting fatter, chances are, you may be gaining weight as well.

The latest study generated by 32 years of data compiled by the Framingham Heart Study shows that social ties are a key factor in the spread of obesity. When an individual gains weight, their friends, spouses and siblings are likely to gain weight as well, according a study published in today's New England Journal of Medicine.

``It's kind of a social contagion, a spread in the social network regarding the norms in what is an acceptable body type,'' said Dr. Nicholas A. Christakis of Harvard Medical School, who co-authored the study with Dr. James H. Fowler of the University of California at San Diego.

Over the last 25 years, the incidence of obesity among adults in the United States has more than doubled, shooting from 15 to 32 percent. Roughly 66 percent of adults are considered overweight.

Using data collected from the Framingham Heart Study since 1971, Christakis and Fowler looked at records for families and traced the friends study participants had listed as contacts. Focusing on 12,067 individuals, including 5,124 Framingham Heart Study participants, they observed a total of 38,611 family ties.

A sedentary lifestyle and increased consumption of high-calorie foods are critical factors in the prevalence of obesity. Both, however, can be influenced by friends and family, leading to obesity, according to the study.

When an individual becomes obese, there is a 57 percent chance that a friend will become obese. Siblings have a 40 percent increased risk of obesity and their spouse has a 37 percent increased risk, the study finds.

In same-sex friendships, individuals experienced a 71 percent increased risk if a friend became obese. This pattern was also observed in siblings; men have a 44 percent chance of becoming obese if his brother is obese. Among sisters, that jumps to 67 percent.

Environment does not appear to be a factor, the researchers found. Neighbors that are not within an individual's social network are not affected, while siblings who live in other parts of the countries but remain in contact are affected.

``We didn't find that people who were overweight simply flocked together,'' Christakis said. ``Rather, we found what seemed to be a spread of obesity and that the likelihood of a person becoming obese depended on the nature of the relationship.''

There is, however, a positive note: The social aspect for weight gain can also work for weight loss, Christakis said. Both authors concluded that obesity needs to be addressed not simply as a clinical problem but also as a social issue.

``We need to understand that a significant part of an individual's health is embedded in their network,'' Fowler said. ``In fact, we really need to revisit our whole notion of cost-effectiveness. The fact that certain health care approaches won't just affect the individual but will also cascade through their social ties means that health care interventions are far more cost-effective than previously thought.''

Christakis said the researchers were impressed by the depth of data available on Framingham Heart Study participants.

``This is a study that could only be done through the Framingham Heart Study,'' Christakis said. ``The Framingham Heart Study is the crown jewel of epidemiology ... this could not be done with any other data set in the world.''